Tsinghua Unigroup, through two wholly owned units, controls an 8.15 percent voting stake, Frankfurt-listed Dialog said in a filing on Thursday. That is up one percentage point since the last disclosure by Dialog on Tuesday.

Tsinghua Unigroup, which has not responded to requests for comment, has in the past been blocked on U.S. national security grounds in its attempts to take over Western chip makers, including Germany's Aixtron SE (>> AIXTRON SE).

Tsinghua Unigroup, now Dialog's largest shareholder, also controls Spreadtrum Communications, a developer of mobile chipset platforms for smartphones with which Dialog cooperates in China.

Dialog acknowledged for the first time on Monday that Apple could develop its own battery-saving chips used in iPhones, fuelling a sell-off that has driven its shares down by 38 percent in the past week.

CEO Jalal Bagherli said, however, there was no risk to Dialog's existing supply deals in 2018 and it was in advanced talks with Apple on designing 2019-type products.